The invention relates to high power piezoelectric ceramics, more particularly, to piezoelectric ceramic compositions for use in ultrasonic motors, ultrasonic vibrators, piezoelectric actuators, and the like.
The art has explored the high-power characteristics of piezoelectric materials for use in devices such as ultrasonic motors, piezoelectric actuators and piezoelectric transformers. It is preferred in the art that the piezoelectric materials used in these types of devices have a high mechanical quality factor, low heat generation, a high piezoelectric constant, as well as high vibrational velocities (vo) when subjected to low AC electric fields. The art has found it difficult, however, to achieve a piezoelectric material which has both a high mechanical quality factor and a high piezoelectric constant, as well as high vibrational velocity.
It is known in the art that the v0 in lead-zirconate-titanate (PZT) compounds which have the ABO3 perovskite structure can be increased by introducing lower valent dopants such as Fe on the B-site, and that v0 can be decreased by introducing higher valent dopants such as Nb on the B-site. The lower valent dopants tend to produce xe2x80x9chardeningxe2x80x9d effects on the base PZT type compounds by increasing the mechanical quality factor (Qm) while decreasing the electromechanical coupling factor (k). In contrast, higher valent substituents tend to decrease the Qm while increasing the (k) value.
It also is known in the art that the vibrational velocity (v0)of a piezoelectric material is restricted by heat generation within the piezoelectric material when subjected to an electric field (Eac). Heat generation under an electric field is known to be a function of vibrational velocity (vo). The value of vo is directly proportional to Qm and to the electromechanical coupling factor (k) under constant Eac. Development of a piezoelectric material with significantly higher vo, however, has not been successful in the art since each of Qm and k are increased at the expense of the other.
A need therefore exists for a piezoelectric material which has both increased Qm and increased k values, as well as increased vibrational velocity for high-power applications.
This invention relates to piezoelectric compositions for manufacture of rare earth (xe2x80x9cRExe2x80x9d) doped Pb(Zr,Ti)O3xe2x80x94Pb(Mn,Sb)O3 compounds which have increased vibrational velocity as well as increased Qm and (k) values. The invention further relates to piezoelectric compounds corresponding to the formula (zPb(ZrwTi(1xe2x88x92w))O3xe2x80x94(1xe2x88x92z)Pb(Mn1/3Sb2/3)O3+REx) where z is xe2x89xa60.95, preferably about 0.90, 0.4xe2x89xa6wxe2x89xa60.6, preferably 0.50xe2x89xa6wxe2x89xa60.54, more preferably about 0.52, and where RE is a rare earth cation dopant, and 0 less than x less than 5%, preferably 0 less than x less than 2%.
The RE dopants employed advantageously generate both xe2x80x9chardeningxe2x80x9d and xe2x80x9csofteningxe2x80x9d effects in the doped Pb(Zr,Ti)O3xe2x80x94Pb(Mn,Sb)O3 compounds. Examples of RE dopants which may be employed include Eu+3, Yb+3, Ce3+, Er3+, Tm3+, Ho3+ and Dy3+, and mixtures thereof, preferably Eu+3, and Yb+3, most preferably Yb+3. The Eu and Yb dopants advantageously produce both xe2x80x9chardeningxe2x80x9d and xe2x80x9csofteningxe2x80x9d effects in Pb(Zr,Ti)O3xe2x80x94Pb(Mn,Sb)O3 compounds such as 0.90Pb(Zr0.52Ti0.48)03xe2x88x920.10Pb(Mn1/3Sb2/3)O3. Doping of 0.90Pb(Zr0.52Ti0.48)03xe2x88x920.10Pb(Mn1/3Sb2/3)O3 with any of Eu and Yb produces increased Qm, d31, and k31 relative to undoped 0.90Pb(Zr0.52Ti0.48)03xe2x88x920.10Pb(Mn1/3Sb2/3)O3. Under high Eac conditions, Eu and Yb doping of Pb(Zr,Ti)O3xe2x80x94Pb(Mn,Sb)O3 type compounds such as 0.90Pb(Zr0.52Ti0.48)03xe2x88x920.10Pb(Mn1/3Sb2/3)O3 advantageously produces an increased v0 relative to undoped 0.90 Pb(Zr0.52Ti0.48)03xe2x88x920.10Pb(Mn1/3Sb2/3)O3. These doped compounds include compounds of formula (zPb(ZrwTi(1xe2x88x92w))O3xe2x88x92(1xe2x88x92z)Pb(Mn1/3Sb2/3)O3+REx) where z is 0.90, w is 0.52, RE is Yb and x is about 0.1 to about 0.3%. Advantageously, Pb(Zr,Ti)O3xe2x80x94Pb(Mn,Sb)O3 type compounds such as 0.90Pb(Zr0.52Ti0.48)O3xe2x88x920.10Pb(Mn1/3Sb2/3)O3, when doped with about 0.1 to about 2.0 wt. % Yb, preferably about 0.1% to about 0.2% Yb, produces a high-power piezoelectric material.
In another aspect, the invention relates to piezoelectric devices such as ultrasonic motors, ultrasonic vibrators, and piezoelectric actuators which include a piezoelectric ceramic compound represented by formula (zPb(ZrwTi(1xe2x88x92w))O3xe2x88x92(1xe2x88x92z)Pb(Mn1/3Sb2/3)O3+REx) where zxe2x89xa60.95, preferably about 0.90, 0.4xe2x89xa6wxe2x89xa60.6, preferably 0.50xe2x89xa6wxe2x89xa60.54, more preferably about 0.52, RE is a rare earth cation such as Yb, Eu and Ce, and 0 less than x less than 5%, preferably 0 less than x less than 2%.
In yet another aspect, the invention relates to piezoelectric ceramic compounds represented by formula (zPb(ZrwTi(1xe2x88x92w))O3xe2x88x92(1xe2x88x92z)Pb(Mn1/3Sb2/3)O3+REx) where z is 0.9, w is 0.52, RE is a rare earth cation selected from the group consisting of Eu, Lu, Nd and La and x is 0.1%.